1. Field of the Invention
The present invention relates to a multilayer optical recording medium having a plurality of recording layers and a recording method and apparatus of the multilayer optical recording medium.
2. Description of the Related Art
In recent years, development of a multilayer optical disc has progressed as a recording medium having a large capacity wherein a recording capacity per side can be increased. The multilayer optical disc has a structure in which a plurality of half-mirror type reflection recording layers are laminated. For example, in a 2-layer DVD (Digital Versatile Disc) having two recording layers, two recording layers are stacked with a relatively small interval. A phase change recording film is formed on each of an upper layer (i.e., a layer near an optical pickup) and a lower layer. Upon recording of the 2-layer disc, a laser beam is focused on one of the recording layers and a data signal is recorded thereon.
It is, however, necessary to change recording conditions when recording is performed on the lower layer according to whether data has been recorded on the upper layer or no data is recorded thereon. This is because an average reflectance of the upper layer increases (i.e., an average transmittance decreases) when data has been recorded on the upper layer. There is, consequently, a problem that a recording density has to be set to a value lower than that used when recording data on a single-layer disc in consideration of a reduction of a S/N ratio (signal to noise ratio) due to an influence of larger average reflectance.
The problem becomes more serious for a multilayer optical disc in which the number of recording layers is further increased in order to increase the recording density. A large difference occurs in the transmittance or the S/N ratio in dependence on whether the recording layers over the recording layer on which recording is performed are recorded layers or not. There is, thus, a problem such that the necessity of sequentially recording data from the upper layer to the lower layer is caused or so many recording layers cannot be laminated.